The invention is generally directed to toner and developer compositions, and more specifically, the present invention is directed to developer and toner compositions containing charge enhancing additives, which impart or assist in imparting a negative charge to the toner particles and enable toners with rapid triboelectric charging characteristics. In embodiments, there are provided in accordance with the present invention toner compositions comprised of a polymer or polymer resins, colorants, such as pigment particles or dye molecules, and certain aluminum or boron charge enhancing additives having a structural moiety derived from N-alkyl or N-aryl bis(hydroxyalkyl)amine. In embodiments, the present invention is directed to toners with certain zinc or boron compounds which enhance or improve the toner's triboelectric charging performance. The zinc compounds are generally prepared by treating a suspension of an aromatic carboxylic acid, preferably hydroxybenzoic acid in an aqueous medium containing a molar equivalent of zinc ion with two or more molar equivalents of a bis(hydroxyalkyl)amine at a temperature ranging from ambient, about 25.degree. C. to about 100.degree. C. The boron compounds can be obtained by the reaction of an alkyl or arylboric acid with an equimolar quantity of a bis(hydroxyalkyl)amine, preferably N-aryl bis(hydroxyethyl)amine, at an elevated temperature, for example from about 75.degree. C. to about 100.degree. C. with azeotropic removal of the water byproduct. The aforementioned charge additives in embodiments of the present invention enable, for example, toners with rapid triboelectric charging characteristics, extended developer life, stable triboelectrical properties irrespective of changes in environmental conditions, and high print quality with substantially no background development. Also, the aforementioned toner compositions usually contain a colorant component comprised of, for example, carbon black, magnetites, or mixtures thereof, color pigments or dyes such as cyan, magenta, yellow, blue, green, red, or brown color, or mixtures thereof thereby providing for the development and generation of black and/or colored images. The toner and developer compositions of the present invention can be selected for electrophotographic, especially xerographic, imaging and printing processes, including color processes. These charge enhancing compounds are believed to have an intramolecular complex or salt structure having a central metal ion, and a quaternary ammonium ligand. Accordingly, the structure of these charge enhancing additives in embodiments are believed to be represented by the general structures (Ia) and (Ib): ##STR1## where R and R' are independently selected from alkyl of 1 to about 20 carbon atoms and aryl of from 6 to about 30 carbon atoms; and R" is an alkylene with from 1 to about 5 carbon atoms, and more specifically, methylene groups.
Toners with negative charge additives are known, reference for example U.S. Pat. Nos. 4,411,974 and 4,206,064, the disclosures of which are totally incorporated herein by reference. The '974 patent discloses negatively charged toner compositions comprised of resins, pigment particles, and as a charge enhancing additive ortho-halophenyl carboxylic acids. Similarly, there are disclosed in the '064 patent toner compositions with chromium, cobalt, and nickel complexes of salicylic acid as negative charge enhancing additives. In U.S. Pat. No. 4,845,003, there are illustrated negatively charged toners with certain aluminum salt charge additives. More specifically, this patent discloses as charge additives aluminum complexes comprised of two or three hydroxybenzoic acid ligands bonded to a central aluminum ion. While these charge additives may have the capability of imparting negative triboelectric charge to toner particles, they are generally not efficient in promoting the rate of triboelectric charging of toner particles. A fast rate of charging is particularly crucial for high speed xerographic machines since, for example, these machines consume toner rapidly, and fresh toner has to be constantly added. The added uncharged toners, therefore, must charge up to their equilibrium triboelectric charge level rapidly to ensure no interruption in the xerographic imaging or printing operation. Another shortcoming of these charge additives is their thermal instability, that is they often break down during the thermal extrusion process of the toner manufacturing cycle. Most or many of these and other disadvantages are eliminated, or substantially eliminated with the zinc complex charge additives of the present invention.
Toner compositions with other negative charge enhancing additives include, for example, U.S. Pat. Nos. 5,300,387 and 5,302,481, the disclosures of which are totally incorporated herein by reference. Specifically, the '387 patent discloses toner compositions comprised of a toner resin, a colorant, optional surface additives, and a metal complex charge additive derived from the reaction of a dicarboxylic acid and a hydroxybenzoic acid with a metal ion. Structurally, these charge enhancing additives are anionic metal complexes containing an anion comprised of a central metal ion, such as aluminum, gallium, zinc, cobalt ion and the like, bonded to two different bidentate ligands derived from an aromatic dicarboxylic acid and a hydroxybenzoic acid, and a countercation of proton, ammonium ion, alkaline metal cation or the like. Similarly, the '481 patent describes toner compositions with aluminum charge additives with mixed ligands derived from hydroxyphenol and hydroxybenzoic acid. While these charge additives are effective in imparting negative charge to toners, their rates of charging are generally not as rapid as those of the additives of the present invention, and their preparative processes are not as simple. Another advantage of the charge additives of the present invention is that can be obtained from economical precursors. There are also disclosed in U.S. Pat. No. 5,409,794, the disclosure of which is totally incorporated herein by reference, toner compositions containing negative charge additives derived from the reaction of a metal, a metal carbonyl, a metal salt, or a metal oxide with a .beta.-diketone, a .beta.-keto ester, or a malonic ester in an aqueous or organic medium. These charge additives render toner compositions negative in triboelectric charging, but their charging rates are generally slower than those of the charge additives of the present invention.
Developer compositions with charge enhancing additives, which impart a positive charge to the toner particles, are also well known. Thus, for example, there is described in U.S. Pat. No. 3,893,935, the disclosure of which is totally incorporated herein by reference, the use of quaternary ammonium salts as charge control agents for electrostatic toner compositions; U.S. Pat. No. 4,221,856, the disclosure of which is totally incorporated herein by reference, which discloses electrophotographic toners containing resin compatible quaternary ammonium compounds; U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, discloses developer compositions containing as charge enhancing additives organic sulfate and sulfonates, which additives can impart a positive charge to the toner composition; and U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, discloses positively charged toner compositions with resins and pigment particles, and as charge enhancing additives alkyl pyridinium compounds.
U.S. Pat. No. 5,275,900, the disclosure of which is totally incorporated herein by reference, describes toner and developer compositions containing metal complex charge additives, which are anionic in nature. More specifically, disclosed in this patent is a negatively charged toner composition comprised of a polymer or polymer resins, a colorant or colorants, optional surface additives, and a metal complex charge enhancing additive obtained from the reaction of a hydroxybenzoic acid and a base with a mixture of a metal ion and a hydroxyphenol; and a negatively charged toner composition comprised of a polymer or polymers, a colorant or colorants, optional surface additives, and a metal complex charge enhancing additive obtained from the reaction of a hydroxybenzoic acid and a base with a mixture of a metal ion and an aromatic dicarboxylic acid. These complexes are comprised of an anion with two bidentate ligands chelating to a central metal, and countercations of protons, alkaline metal ions, ammonium ions, and the like.
U.S. Pat. No. 5,290,651 discloses another class of charge enhancing additives which are based on zinc complexes of hydroxybenzoic acid and hydroxyphenol, the disclosures of which are totally incorporated herein by reference. Specifically, these complexes, when incorporated into toner compositions comprised of a polymer or polymer resins, a colorant or colorants, optional surface additives, and a zinc complex enhanced the level of negative triboelectric charge of the toner compositions.
Additionally, novel metal complex negative charge enhancing additives for toner compositions are disclosed in U.S. Pat. Nos. 5,300,387; 5,302,481 and 5,332,636, the disclosures of which are totally incorporated herein by reference. These complexes have the capability of being able to enhance both the rate of charging and the negative triboelectric charge levels of toner compositions.
Although many charge enhancing additives are known, there continues to be a need for charge enhancing additives which, when incorporated in toners, provide toners with many of the advantages illustrated herein. There is also a need for negative charge enhancing additives which are useful for incorporation into black and colored toner compositions which can be utilized for developing positive electrostatic latent images. Moreover, there is a need for colored toner compositions containing charge enhancing additives which do not interfere with the color quality of the colorants present in the toners. Another need relates to the provision of toner compositions with certain charge enhancing additives, which toners in embodiments thereof possess substantially stable triboelectric charge levels, and display acceptable rates of triboelectric charging characteristics. Furthermore, there is also a need for toner compositions with certain charge enhancing additives which possess excellent dispersibility characteristics in toner resins, and can, therefore, form stable dispersions in the toner compositions. There is also a need for negatively charged black and colored toner compositions that are useful for incorporation into various imaging processes, inclusive of color xerography, as illustrated in U.S. Pat. No. 4,078,929, the disclosure of which is totally incorporated herein by reference; laser printers; and additionally a need for toner compositions useful in imaging apparatuses having incorporated therein layered photoresponsive imaging members, such as the members illustrated in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. Also, there is a need for negative toner compositions which have desirable triboelectric charge levels of, for example, from between about -10 to about -40 microcoulombs per gram, and preferably from about -10 to about -25 microcoulombs per gram, and triboelectric charging rates of less about 60 seconds, and preferably less than 45 seconds as measured by standard charge spectrograph methods when the toners are frictionally charged against suitable carrier particles via conventional roll milling techniques. There is also a need for environmentally compatible charge enhancing additives which when incorporated at effective concentrations of, for example, less than 10 weight percent, preferably less than 5 weight percent in toners, provide toners that are environmentally acceptable. An additional need resides in the provision of simple and cost-effective preparative processes for the charge enhancing additives of the present invention. The concentrations of the charge additives that can be incorporated into the toner compositions generally range from about 0.05 weight percent to about 10 weight percent, depending on whether the charge additive is utilized as a surface additive or as a dispersion in the bulk of the toner. The effective concentrations of toner in the developer, that is toner and carrier particles, are, for example, from about 0.5 to about 5 weight percent, preferably from about 1 to about 3 weight percent.
Illustrated in copending patent applications U.S. Ser. No. 523,576, filed Sep. 5, 1995, is a toner composition comprised of toner resins, colorants, optional surface additives, and a charge enhancing additive obtained from the reaction of an aluminum ion-containing compound with a molar equivalent of an aromatic carboxylic acid, and an excess of an N-alkyl or N-aryl-substituted bis(hydroxyalkyl)amine in an aqueous medium at a temperature ranging from about 25.degree. C. to about 100.degree. C.; and U.S. Ser. No. 523,577, filed Sep. 5, 1995, is a negatively charged toner composition comprised of toner resins, colorants, optional surface additives, and a metal charge enhancing additive obtained from the reaction of a metal ion with a molar equivalent of an ortho-hydroxyphenol and two molar equivalents of an aromatic carboxylic acid in an aqueous medium in the presence of a base, the disclosures of which are totally incorporated herein by reference.